Computers, such as desk top computers, typically comprise a monitor, keyboard or other input device, and a chassis which houses the memory, I/O interfaces, chipsets and the processor. As the cost and size of processors decrease, it may be desirable to house several processors in a single chassis and couple the processors together with a bus. The plurality of processors may then process data more quickly and/or may process multiple streams of data simultaneously. The bus may include several connectors, each of which is configured to be coupled to the processor terminals so that several processors may simultaneously be coupled to the bus. The bus may accordingly comprise a plurality of transmission lines, each corresponding to one of the processor terminals. The transmission lines may include data lines, control signal lines, address lines and power lines.
One problem with the above approach for coupling several processors is that the signals traveling along the transmission lines may reflect at the ends of the bus, potentially altering the data transmitted by the bus. One approach to solving the foregoing problem is to terminate the transmission lines with a termination circuit. The termination circuit may comprise a resistor or a resistor/capacitor circuit that is coupled between the transmission line and a selected voltage.
In one application of the foregoing approach, the termination circuits may be placed on a motherboard within the chassis. One problem with this method is that the termination circuits may consume a large portion of the surface area of the motherboard, which might otherwise be used for additional processors, memory, I/O interfaces, or other performance-enhancing components. Another problem is that if the bus contains several connectors, less than all of which are populated with processors, the termination circuits may be separated from the processor by a significant distance. This may be disadvantageous because signal reflections on the bus may not be adequately reduced by the distant termination circuits.
One approach to solving the above problem has been to place the termination circuits on a card which supports the processor and which is coupled to the bus. One problem with this approach may be that if only one of several connectors of the bus is populated with a processor, termination is provided at only one end of the bus. Accordingly, reflections may still occur at the opposite end of the bus which, as discussed above, may have a deleterious effect on the signals transmitted along the transmission lines of the bus.
Another problem with conventional processor and bus arrangements is that processor upgrade circuits and other peripheral circuitry, such as decoupling capacitors, may be positioned on the motherboard. These circuits may take up a significant portion of the motherboard surface area, which might other wise be used for other components.